Hepatitis B virus (HBV) is a noncytopathic enveloped virus with a small, circular double stranded DNA genome. HBV infection causes acute and chronic liver disease and hepatocellular carcinoma. Although it is generally thought that clearance of HBV from infected livers is mediated primarily by antigen specific cytotoxic T cell that destroy infected hepatocytes, recent studies using a transgenic mouse system of HBV infection have shown that transferred virus- specific cytotoxic T cells can abolish hepatitis B virus gene expression and replication in the liver without killing the hepatocytes. This effect is mediated by interferon-gamma and tumor necrosis factor-alpha, which are secreted by the cytotoxic T lymphocytes following antigen recognition. Thus, it is hypothesized that cytokines play a major role in viral clearance. However, cytokine responses during a natural acute infection of HBV have not yet been characterized. Moreover, validity of the overall hypothesis needs to be evaluated in a natural host system. Therefore, it is the goal of this proposal to address these issues in a natural host. The probes to detect woodchuck TNF-alpha and INF-gamma genes will be developed by RT-PCR. The pattern of TNF-alpha and INF-gamma cytokine expression will by analyzed via norther blot or RNase protection assay. The correlation between the profile of cytokine expression and the viral clearance will be examined. The type of infiltrating cells that contribute to the cytokine effect also will be investigated by in situ hybridization. Finally, the effect of TNF- alpha and INF-gamma will be determined via expressing them from an adeno vector in chronic infected liver and administering monoclonal antibodies against TNF-alpha or INF-alpha to block their activities in vivo.